Exercise ball



FIG. 1 is a front perspective view of an exercise ball.

FIG. 2 is a front view thereof.

FIG. 3 is a rear view thereof.

FIGS. 4 and 5 are opposing side views thereof.

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken lines shown in the figures are for the purpose of illustrating portions of the exercise ball, which form no part of the claimed design. 

CLAIM The ornamental design for an exercise ball, as shown and described. 